Sunderland is a UK outlier in how we deliver RRT to our patients, predominately using renal specialist prescribed dialysis (often SLED) rather than critical care physician prescribed CVVHF.Clearly we feel there is a benefit to this practice, but as an outlier we should be mindful that we’re not blindly carrying on when we shouldn’t.

The CONVINT trial is the latest to compare CVVHF to IHD in the critical care population.

The evidence in this area is not great; whilst there’s evidence out there the quality can and has been criticised.The best we had until now is probably this paper from 2009.This group randomised 316 patients to IHD or CVVHF, and found no difference in any of their outcome measures including hospital mortality (OR 0.83 p=0.43).The study certainly had its weaknesses, not least that their power calculation required n=407 in each arm.Their explanation for not achieving these numbers is brutally honest if not politically put: “motivation declined and policy changed considerably during the 3 years of the study”; basically everyone had had enough and wanted to go home!They also describe a fundamental issue with conducting RCTs in this area, which is finding units who use both modalities and who feel there is equipoise. The CONVINT trial therefore should be forgiven for being monocentric.They conducted the trial over nearly 6 years, and needed 200 patients per arm.Unfortunately, they did not achieve their target either (128, 122).The reason given was “a major change in RRT equipment and procedures beyond the investigators control”, which included a shift towards haemodiafiltration.You can only imagine the mood in the meeting when that was decided!If nothing else the evidence in this area demonstrates what a thankless and impossible task research is.

There were no differences in any outcome between the groups.The outcome is given as an odds ratio, which it may be worth refreshing your memory about.The concept of odds can be confusing despite it being a term used freely in conversation. The odds of an event are different to the risk of an event.Where risk is incidence / no of events, odds are incidence of event / incidence of non-event.Risk is dependent on sample size, which in a cohort study (such as this) is determined by the trial design and therefore can’t be used.For this study, the event is death at 14 days after RRT, which occurred in 60.5% of the IHD group and 56.1% of the CVVHF group.The odds of death in the IHD group are therefore 60.5/39.5 = 1.53 and in the CVVHF group 56.1/43.9 = 1.28.The odds ratio is the ratio of these numbers (which can be done either way round in this study because there isn’t really an intervention and control group).The ORR therefore is 1.53/1.28 = 1.20 or 1.28/1.53=0.84.To give a confidence interval for an OR there’s a formula, or a stats package will just churn it out.For this OR of 0.84 the 95% CI is 0.49 to 1.41.This means we are 95% sure that the true OR is between these numbers.Any CI for OR that includes 1 will be non-significant, so the p value of 0.50 is not surprising. This study used intention to treat, which as you know means that whichever group you are randomised to is the group your results belong to. Intention to treat analysis is generally considered to be a good thing.In this study however it’s worth noting that 46% of the CVVHF group crossed over to IHD (what do you think the implications of this might be?).The most common reason was a desire to mobilise or clinical improvement (39%), followed by repeated filter clotting (27%).This highlights some of the reasons we like IHD; it frees the patient up from the machine, there’s no need to switch modality, and there’s not a filter clotting every 10 minutes.On the latter note, 88% of prescribed dose was delivered, which is pretty typical in studies involving CVVHF.While I’m on my soapbox, I also like that we have our RRT overseen by a renal medicine consultant so the patient gets early expertise and continuity of care if still requiring RRT at discharge – any effects of this on outcome will not be included in this study.

Another quite interesting point about this paper is that approx. a quarter of the patients were still needing / getting RRT 60 days after their first treatment.That is higher than the number I quote to families, and wonder if we should look to see what our numbers are – volunteers please!

As always I’d appectiate your comments.What do you think are the advantages and disadvantages to way RRT is delivered around the region?Should we use CVVHF like everyone else?Should everyone else use dialysis? Does it matter at all?

Addendum (6/1/15) - Andy Morrison has given me his presentation entitled "RRT in critical care" which goes a little bit more into some of the other work in this area - it can be found here.

This study replicates many others in the field. There is no demonstrable difference but there are enough methodological flaws to maintain the debate.

There are polarised views in this field as a whole and it is clear that there are a greater number of continuous enthusiasts who are prolific publishers (says an intermittent enthusiast).

There is the potential for significant bias. The "need" for RRT is too broad (and when to start is a whole other topic). There is not necessairily a consistent approach to "dose" (though the miniumum dose is more clearly definied in this setting for continuous therapy). The rationale for switching simply reflects the personal opinions that the study was designed to address. As outlined it makes an ITT analysis impossible.

It is a little odd that it was terminated because of the introduction of further therapies, whose benefit remains anecdotal (HDF). Why they felt compelled to move?

This confirms my position (so it must be right) that for most patients the best treatment is that which can be delivered effectively and in a timely fashion. Logisitics and cost both come into this.

Reply

John G

5/1/2015 08:09:22 am

Whilst I agree the evidence is flimsy I am happy to continue our system. Afterall, if we have a case where we consider filtration would be beneficial (eg severe sepsis in the previously fit & young) our renal colleagues are usually happy to supply it.

Reply

Simon

6/1/2015 04:59:25 am

Given that this paper doesn't seem to show any difference between the two modalities (although with the limitations already discussed) I think it probably comes down to being good at what you do regularly.

As a (previous!) ICCU resident I certainly preferred HD. There seemed to be fewer issues, than with CVVHF, that required my attention - fewer line issues, fewer alarms (better for everyone's sanity!) but this is purely ancedotal.

HD obviously places an extra burden on the renal team but as Pete mentions it will ease their transition into renal care long term, if needed, and presumably means our ICCU nurse is free to care for the patient rather than the apparently greater and more frequent needs of the CVVHF machine!

Reply

sean fenwick

7/1/2015 02:01:10 am

This study replicates many others in the field. There is no difference but there are enough methodological flaws to maintain the debate.

There are polarised views in this field as a whole and it is clear that there are a greater number of continuous enthusiasts who are prolific publishers.

There is the potential for significant bias. The "need" for RRT is too broad (and when to start is a whole other topic). There is not necessairily a consistent approach to "dose" (though the miniumum dose is more clearly definied in this setting for continuous therapy). The rationale for switching simply reflects the personal opinions that the study was designed to address. As outlined it makes an ITT analysis impossible.

It is a little odd that it was terminated because of the introduction of further therapies, whose benefit remains anecdotal (HDF). Why they felt compelled to move?

This confirms my position (so it must be right) that for most patients the best treatment is that which can be delivered effectively and in a timely fashion. Logisitics and cost both come into this.